Clinical and laboratory studies are conducted to determine etiology (infection, immunity and/or genetics) of chronic diseases of the peripheral and central nervous system. Currents studies include amyotrophic lateral sclerosis, (ALS), polymyositis/dermatomyositis, new post-polio muscle weakness, demyelinating polyneuropathies, neuromuscular complications of AIDS, certain metabolic muscle diseases and Duchenne's muscular dystrophy. Combined clinical data and studied of virus serology and virus isolation are performed. A neuromuscular disease that occurs in patients who have had poliomyelitis at an early age (post-polio syndrome) has been clinically defined along with the rate of progression, the electrophysiological, virological and histochemical findings. The spectrum of neuromuscular disorders associated with HIV infection is being systemically studied and the role of HIV in the pathogenesis of neuropathies and myopathies in HIV-positive patients is investigated. A pilot therapeutic study using AZT for the treatment of HIV-related neuromuscular disease is conducted. Patients with polymyositis are studied and the muscle changes before and after a randomized double-blind controlled study with cyclophosphamide, plasmapheresis or lymphocytphoresis are investigated. Muscle biopsies from patients with Duchenne's muscular dystrophy are studied biochemically to define abnormal proteins (i.e. nebulin). The metabolic activity of the cortex in ALS patients was studied using the PET scan and 18 FDG; hypometabolism was demonstrated not only in the motor but throughout the cortex, suggesting that ALS is a generalized process affecting many cortical regions. These metabolic abnormalities were correlated with pathology of the cortical neurons. Muscle biopsies from patients with nephropathic cystinosis and renal Fanconi syndrome were studied morphologically and biochemically. Signs of a lipid storage myopathy due to carnitine deficiency were found; this has prompted a therapeutic study with carnitine replacement.